Electron discharge tube



Feb. 25, 1947.

J. H. FREMLIN IELECTRON DISCHARGE TUB?!- Filed Sept. 11, "19.42

A 1 mm A Tram 5y v Patented Feb. 25, 1947 ELECTRON DISCHARGE. TUBE .iohn Heaver Fremlin, London W. C. 2, England, assignor to Standard Telephones and Cables, Limited, London, England, a British company Application September 11, 1942, Serial No. 458,055 In Great Britain February 21, 1941 3 Claims. (Cl. 250-2'7.5)

1 At wavelengths of the order of a few cm. it is usually impossible to use conventional circuits in oscillation generators. The resonant impedance of such circuits, owing to excessive radia-.

tion, is usually far too low. As is well known therefore, it is now usual to use lumped circuits of the hollow resonator type which are directly excited by an electron stream, These make it possible to obtain high outputs at extremely short wavelengths. They have, however, the disadvantage that their frequencies are controlled by their physical dimensions which are diflicult to vary conveniently in sealed ofl tubes.

A system of construction is here proposed by means of which the frequency of a single circuit velocity modulated tube of the concentric line type may easily be varied over a wide range without involving relative movement of different parts of the evacuated part of the system.

According to one feature of the invention a resonant circuit adapted to form part of an electron discharge device comprises a short length of transmission line constituted by a central rod or conductor surrounded by a plurality of parallel rods or conductors.

According to another aspect of the invention in a co-axial line resonator circuit for an electron discharge tube, the outer member comprises a plurality of parallel rods or conductors arranged in a circle about the central rod or conductor.

In a particular application of the invention, a structure of the above-defined kind constitutes, in an electron discharge tube of the electron velocity modulated type the resonator through which the electron beam is fired.

In the accompanying drawing which shows, by way of example, one embodiment of the invention, Figure l is a sectional view of a velocity modulated tube taken along the major axis of the tube and Figure 2 is a section taken along the line 2-2 of Figure l.

The external cylinder of a single circuit tube of the kind described in United States Patent No. 2,320,860 is replaced by a number of parallel rods I arranged symmetrically around the centre line 2. If these rods are close enough together, the resonant impedance of the line is but slightly reduced. These rods, together with the rod forming the centre line, are brought out through base 3 of the vacuum envelope 4 as a ring seal of known type.

On these rods then may be placed a sliding bridge 6 of the form shown which makes an effective low resistance short circuit of the line.

By moving this short circuit it is clearly possible to vary the frequencies to which the whole line would be resonant, and thus to tune the system to any desired frequency over a considerable range. In Figure 1 the centre line is shown cut off beyond the working point; in this case the total effective length between this end and the shorting bridge will be where A is the wavelength to which the resonator is tuned and n is an integer.

When the variation of frequency required is not too great, the centre line could be continued and short circuited to the outer line at from the middle of the working section. This would double the power output available at the mean wavelength but would reduce the tuning range more and more as n increases.

It is advantageous to arrange the glass seal near a voltage node for the mean wavelength of the desired range in order to reduce as far as possible, dielectric losses in the vacuum envelope.

Referring again to the drawing, 5 is a cathode, 7 a shield electrode and 8 a grid electrode, gap-forming fins 9 and H] are provided between pairs of the outer rods I and on the inner rod 2 along a diameter of the structure.

What is claimed is:

1. Electron discharge tube of the electron velocity modulation type comprising an envelope, a glass disk seal closing said envelope, a central conductor and a plurality of parallel conductors in a circle about said central conductor, said central conductor and plurality of parallel conductors being sealed through said disk seal and constituting a co-axial line resonator extending partly within and partly without said envelope, means inside said envelope for passing a beam of electrons diametrically across said co-axial line resonator and for effecting velocity modulation of the electrons in said beam and a slidable conducting bridge member fitting over said conductors outside said envelope for tuning said resonator.

2. Electron discharge tube of the electron ve locity modulation type comprising an envelope, a glass disk seal closing said enevelope, a central .conductor and a plurality of parallel conductors in a circle about said central conductor, said centuti'ng' a co-axial'line resonator extending partly within and partly without said envelope, fins mounted on said central conductor and on pairs of said plurality of parallel conductors Within said enevelope, said fins defining a diametral passage across said coaxial line resonator, means for passing a beam of electrons through said diametral passage and thereby efiecting velocity modulation of the electrons in said beam, and a ,slidable conducting bridge member fitting over said'conductors outside said envelope for tuning said resonator.

3. Electron discharge tube of the velocity modulation type comprising an envelope, a cen-\ tral conductor and a plurality of parallel conductors in a circle about said central conductor, said central conductor and plurality of parallel conductors being sealed through said envelope and. constituting a co-axial line resonator, fins mounted on said central conductor and on pairs of 4 r said plurality of parallel conductors Within said envelope, saidfins defining a diametral passage across said co-axia-l line resonator, means for passing a beam of electrons through said diametral passage and thereby efiecting velocity modulation of the electrons in said beam, and means for tuning said co-axial line resonator.

' JOHN HEAVER REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,289,846 Litton July 14, 1942 2,338,306 Smyth Jan. 4, 1944 1,750,386 Brown Mar, 11, 1930 2,287,845 Varian et al June 30, 1942 

